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  • Conference paper
    Chen W, Lin ZL, Griebner U, Murray RT, Mateos X, Loiko P, Pan Z, Zhang G, Petrov Vet al., 2024,

    Phase- and group-locked vector solitons in a femtosecond mode-locked Ho-laser

    Group-velocity locked vector solitons are observed in a mode-locked femtosecond solid-state laser at ~2 μm. Under certain conditions, stable phase-locking of the two polarizations occurs in the soliton regime: a phase- and group-locked vector soliton.
  • Conference paper
    Wang Y, Battle RA, Simon D, Xiang Y, Azevedo Magalhaes SF, Robinson KN, Runcorn TH, Takats Z, Murray RTet al., 2024,

    Laser Ablation of Biological Tissue with a 2.94 μm Picosecond Optical Parametric Amplifier for Ambient Mass Spectrometry Imaging

    We report a 2.94 μm OPA with ∼100 ps pulse duration, 400 nJ pulse energy and a 500 kHz repetition rate, which enables high resolution (≤10 μm) laser desorption-based mass spectrometry imaging of biological tissue.
  • Conference paper
    Zeng HJ, Xue WZ, Murray RT, Cui C, Wang L, Pan Z, Loiko P, Mateos X, Zhang G, Griebner U, Petrov V, Chen Wet al., 2024,

    In-Band Pumped Kerr-Lens Mode-Locked Tm,Ho-codoped Calcium Aluminate Laser

    We report on a Kerr-lens mode-locked Tm,Ho,Lu:CaGdAlO<inf>4</inf> laser, in-band pumped by a fiber Raman laser at 1678 nm. 79-fs pulses were generated at 2073.6 nm with an average power of 91 mW at 85.7 MHz.
  • Conference paper
    Chen W, Lin ZL, Griebner U, Murray RT, Mateos X, Loiko P, Pan Z, Zhang G, Petrov Vet al., 2024,

    Phase- and group-locked vector solitons in a femtosecond mode-locked Ho-laser

    Group-velocity locked vector solitons are observed in a mode-locked femtosecond solid-state laser at ~2 μm. Under certain conditions, stable phase-locking of the two polarizations occurs in the soliton regime: a phase- and group-locked vector soliton.
  • Conference paper
    Koufidis SF, Koutserimpas TT, Monticone F, McCall MWet al., 2024,

    Time-Periodic Optical Activity

    , 18th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), Publisher: IEEE, ISSN: 2573-2684
  • Conference paper
    Runcorn TH, Murray RT, Taylor JR, 2024,

    Multi-watt red nanosecond frequency-doubled Raman-shifted fiber laser

    , Conference on Nonlinear Frequency Generation and Conversion - Materials and Devices XXIII, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
  • Conference paper
    De Vries M, Naidoo R, Fourkioti O, Dent LG, Curry N, Dunsby C, Bakal Cet al., 2024,

    Interpretable Phenotypic Profiling of 3D Cellular Morphodynamics

    , 27th International Conference on Medical Image Computing and Computer Assisted Intervention (MICCAI), Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 481-491, ISSN: 0302-9743
  • Conference paper
    Krawczyk B, Kudlinski A, Battle RA, Murray RT, Runcorn THet al., 2024,

    Enhancement of four-wave mixing via stimulated emission in a Yb-doped photonic crystal fiber

    , Conference on Fiber Lasers XXI - Technology and Systems, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
  • Journal article
    Paie P, Calisesi G, Candeo A, Comi A, Sala F, Ceccarelli F, De Luigi A, Veglianese P, Muhlberger K, Fokine M, Valentini G, Osellame R, Neil M, Bassi A, Bragheri Fet al., 2023,

    Structured-light-sheet imaging in an integrated optofluidic platform

    , LAB ON A CHIP, Vol: 24, Pages: 34-46, ISSN: 1473-0197
  • Journal article
    Liang M, Minassian A, Damzen MJ, 2023,

    High-energy acousto-optic Q-switched alexandrite laser with wavelength tunable fundamental and UV second harmonic generation

    , Optics Express, Vol: 31, Pages: 42428-42438, ISSN: 1094-4087

    We investigate high-energy mJ-class diode-pumped acousto-optic (AO) Q-switched alexandrite lasers with broad tunability at both the fundamental near-IR wavelength range and second harmonic generation (SHG) in the UV wavelength range. An AO Q-switched alexandrite laser with continuous-wave diode-pumping has been operated at up to 10 kHz and producing pulse energy of 700 µJ at repetition rate of 1 kHz. With pulsed double-pass diode-pumping, we demonstrate higher pulse energy of 2.6 mJ. With wavelength tuning, this laser system demonstrated broad fundamental tuning range from 719 to 787 nm with diffraction-limited beam quality (M2 = 1.05). By external cavity second harmonic generation in a Type-I LBO crystal, pulse energy of 0.66 mJ is generated at 375 nm and with UV tuning range from 361 to 391 nm. To our knowledge, this is the first demonstration of AO Q-switched alexandrite laser with broad wavelength tuning in the near-IR and UV wavelength ranges and shows its excellent potential as a pulsed source for future applications.
  • Journal article
    Zeng H, Xue W, Murray RT, Chen W, Pan Z, Wang L, Cui C, Loiko P, Mateos X, Griebner U, Petrov Vet al., 2023,

    Continuous-wave and mode-locked operation of an in-band pumped Tm,Ho,Lu:CaGdAlO₄ laser

    , Applied Sciences, Vol: 13, ISSN: 2076-3417

    We investigate in-band pumping of a Tm,Ho,Lu:CaGdAlO4 laser using a Raman-shifted Er-fiber laser (1678 nm), in the continuous-wave (CW) and mode-locked (ML) regimes. A maximum output power of 524 mW is obtained in the CW regime with a 5% output coupler at an absorbed pump power of 2.04 W, corresponding to a slope efficiency of 27.9%. A maximum CW wavelength tuning range of 160 nm at the zero level, from 1984 to 2144 nm, is obtained with a 0.2% output coupler. In the ML regime, pumping with 5.5 W (unpolarized), the average output power (0.2% output coupler) reaches 148 mW at a repetition rate of ~96 MHz. The output spectrum is centered at 2071.5 nm with a FWHM of 21.5 nm (σ-polarization). The pulse duration amounts to 218 fs (time-bandwidth product equal to 0.327).
  • Journal article
    Mechem CC, Boyle TL, Simmons MA, McCall MW, Sammon Met al., 2023,

    An EMS Response to Refugees Arriving at an International Airport: A Report From the Field

    , DISASTER MEDICINE AND PUBLIC HEALTH PREPAREDNESS, Vol: 17, ISSN: 1935-7893
  • Journal article
    Koufidis SFR, Mccall MW, 2023,

    Wavelength-independent Bragg-like reflection in uniaxial bi-anisotropic media

    , JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, Vol: 40, Pages: 2829-2841, ISSN: 0740-3224
  • Journal article
    Lightley J, Kumar S, Lim MQ, Garcia E, Goerlitz F, Alexandrov Y, Parrado T, Hollick C, Steele E, Rossmann K, Graham J, Broichhagen J, Mcneish IA, Roufosse CA, Neil MAA, Dunsby C, French PMWet al., 2023,

    <i>openFrame</i>: A modular, sustainable, open microscopy platform with single-shot, dual-axis optical autofocus module providing high precision and long range of operation

    , JOURNAL OF MICROSCOPY, Vol: 292, Pages: 64-77, ISSN: 0022-2720
    • Cite
    • Citations: 15
  • Journal article
    Hong W, Sparks H, Dunsby C, 2023,

    Alignment and characterisation of remote-refocusingsystems

    , Applied Optics, Vol: 62, Pages: 7431-7440, ISSN: 1559-128X

    The technique of remote refocusing is used in optical microscopy to provide rapid axial scanning without mechanically perturbing the sample and in techniques such as oblique plane microscopy that build on remote refocusing to image a tilted plane within the sample. The magnification between the pupils of the primary (O1) and secondary (O2) microscope objectives of the remote-refocusing system has been shown previously by Mohanan and Corbett [J. Microsc. 288, 95 (2022) [CrossRef] ] to be crucial in obtaining the broadest possible remote-refocusing range. In this work, we performed an initial alignment of a remote-refocusing system and then studied the effect of axial misalignments of O1 and O2, axial misalignment of the primary tube lens (TL1) relative to the secondary tube lens (TL2), lateral misalignments of TL2, and changes in the focal length of TL2. For each instance of the setup, we measured the mean point spread function FWHMxy of 100 nm fluorescent beads and the normalized bead integrated fluorescence signal, and we calculated the axial and lateral distortion of the system; all of these quantities were mapped over the remote-refocusing range and as a function of lateral image position. This allowed us to estimate the volume over which diffraction-limited performance is achieved and how this changes with the alignment of the system.
  • Journal article
    Koufidis SF, Koutserimpas TT, McCall MW, 2023,

    Temporal analog of Bragg gratings

    , OPTICS LETTERS, Vol: 48, Pages: 4500-4503, ISSN: 0146-9592
  • Book chapter
    McCall MW, Kinsler P, Gratus J, 2023,

    A novel approach to electromagnetic constitutive relations

    , Adventures in Contemporary Electromagnetic Theory, Pages: 33-60

    We take a fresh look at electromagnetic constitutive relations, questioning the standard approach that relates the fundamental electromagnetic fields E and B to the excitation fields D and H. Instead, in recognition of the fact that the excitation fields are not directly measurable, we set up a framework that relates the medium response directly to the fundamental fields. We do this in the simplest way, basing the relationship on first-order operators acting on E and B. This relationship, together with Faraday's law, the absence of magnetic monopoles, and local charge conservation, forms the basis of our approach. The laws of Ampère and Gauss, which in the conventional macroscopic formulation of Maxwell's equations contain D and H, are dispensed with. As well as reproducing conventional macroscopic electromagnetic theory in the appropriate limit, we show that this approach admits a richer gamut of possibilities of meta-media than does the conventional approach. In particular, we identify novel axion-like terms and discuss how these might be experimentally realized. Tracing our approach back to vacuum, we admit the possibility of an axion-like term augmenting the conventional vacuum constitutive relations. We show that it has a topological character, one that can be exploited by manipulation of the background spacetime manifold. In a simple model setting, we show that a careful examination of the mathematical basis of Stokes' theorem leads to a severance of the link between local and global charge conservation.
  • Journal article
    Tawy G, Davidson NP, Churchill G, Damzen MJ, Smith PGR, Gates JC, Gawith CBEet al., 2023,

    Temperature-tunable UV generation using an Alexandrite laser and PPLN waveguides

    , OPTICS EXPRESS, Vol: 31, Pages: 22757-22765, ISSN: 1094-4087
  • Journal article
    Taylor JR, 2023,

    Early optical soliton research at Imperial College London

    , OPTICS COMMUNICATIONS, Vol: 536, ISSN: 0030-4018
  • Journal article
    Codescu M-A, Kunze T, Weiß M, Brehm M, Kornilov O, Sebastiani D, Nibbering ETJet al., 2023,

    Ultrafast Proton Transfer Pathways Mediated by Amphoteric Imidazole

    , The Journal of Physical Chemistry Letters, Vol: 14, Pages: 4775-4785, ISSN: 1948-7185
  • Journal article
    Smith M, Sparks H, Almagro J, Chaigne A, Behrens A, Dunsby C, Salbreux Get al., 2023,

    Active mesh and neural network pipeline for cell aggregate segmentation

    , Biophysical Journal, Vol: 122, Pages: 1586-1599, ISSN: 0006-3495

    Segmenting cells within cellular aggregates in 3D is a growing challenge in cell biology due to improvements in capacity and accuracy of microscopy techniques. Here, we describe a pipeline to segment images of cell aggregates in 3D. The pipeline combines neural network segmentations with active meshes. We apply our segmentation method to cultured mouse mammary gland organoids imaged over 24 h with oblique plane microscopy, a high-throughput light-sheet fluorescence microscopy technique. We show that our method can also be applied to images of mouse embryonic stem cells imaged with a spinning disc microscope. We segment individual cells based on nuclei and cell membrane fluorescent markers, and track cells over time. We describe metrics to quantify the quality of the automated segmentation. Our segmentation pipeline involves a Fiji plugin that implements active mesh deformation and allows a user to create training data, automatically obtain segmentation meshes from original image data or neural network prediction, and manually curate segmentation data to identify and correct mistakes. Our active meshes-based approach facilitates segmentation postprocessing, correction, and integration with neural network prediction.
  • Journal article
    Riemer K, Toulemonde M, Yan J, Lerendegui M, Stride E, Weinberg PD, Dunsby C, Tang M-Xet al., 2023,

    Fast and selective super-resolution ultrasound in vivo with acoustically activated nanodroplets

    , IEEE Transactions on Medical Imaging, Vol: 42, Pages: 1056-1067, ISSN: 0278-0062

    Perfusion by the microcirculation is key to the development, maintenance and pathology of tissue. Its measurement with high spatiotemporal resolution is consequently valuable but remains a challenge in deep tissue. Ultrasound Localization Microscopy (ULM) provides very high spatiotemporal resolution but the use of microbubbles requires low contrast agent concentrations, a long acquisition time, and gives little control over the spatial and temporal distribution of the microbubbles. The present study is the first to demonstrate Acoustic Wave Sparsely-Activated Localization Microscopy (AWSALM) and fast-AWSALM for in vivo super-resolution ultrasound imaging, offering contrast on demand and vascular selectivity. Three different formulations of acoustically activatable contrast agents were used. We demonstrate their use with ultrasound mechanical indices well within recommended safety limits to enable fast on-demand sparse activation and destruction at very high agent concentrations. We produce super-localization maps of the rabbit renal vasculature with acquisition times between 5.5 s and 0.25 s, and a 4-fold improvement in spatial resolution. We present the unique selectivity of AWSALM in visualizing specific vascular branches and downstream microvasculature, and we show super-localized kidney structures in systole (0.25 s) and diastole (0.25 s) with fast-AWSALM outdoing microbubble based ULM. In conclusion, we demonstrate the feasibility of fast and selective measurement of microvascular dynamics in vivo with subwavelength resolution using ultrasound and acoustically activatable nanodroplet contrast agents.
  • Journal article
    Gleneadie HJJ, Fernandez-Ruiz B, Sardini A, Van de Pette M, Dimond A, Prinjha RKK, McGinty J, French PMW, Bagci H, Merkenschlager M, Fisher AGGet al., 2023,

    Endogenous bioluminescent reporters reveal a sustained increase in utrophin gene expression upon EZH2 and ERK1/2 inhibition

    , COMMUNICATIONS BIOLOGY, Vol: 6
  • Journal article
    McCall MW, Koufidis SF, 2023,

    Broadband Bragg phenomenon in a uniform birefringent medium

    , OPTICS LETTERS, Vol: 48, Pages: 1096-1099, ISSN: 0146-9592
  • Journal article
    Tawy G, Minassian A, Damzen MJ, 2023,

    Power-scaled CW Alexandrite lasers

    , APPLIED PHYSICS B-LASERS AND OPTICS, Vol: 129, ISSN: 0946-2171
  • Journal article
    Dvinskikh L, Sparks H, Brito L, MacLeod K, Harding S, Dunsby Cet al., 2023,

    Remote-refocusing light-sheet fluorescence microscopy enables 3D imaging of electromechanical coupling of hiPSC-derived and adult cardiomyocytes in co-culture

    , Scientific Reports, Vol: 13, Pages: 1-14, ISSN: 2045-2322

    Improving cardiac function through stem-cell regenerative therapy requires functional and structural integration of the transplanted cells with the host tissue. Visualizing the electromechanical interaction between native and graft cells necessitates 3D imaging with high spatio-temporal resolution and low photo-toxicity. A custom light-sheet fluorescence microscope was used for volumetric imaging of calcium dynamics in co-cultures of adult rat left ventricle cardiomyocytes and human induced pluripotent stem cell-derived cardiomyocytes. Aberration-free remote refocus of the detection plane synchronously to the scanning of the light sheet along the detection axis enabled fast dual-channel 3D imaging at subcellular resolution without mechanical sample disturbance at up to 8 Hz over a ∼300 µm × 40 µm × 50 µm volume. The two cell types were found to undergo electrically stimulated and spontaneous synchronized calcium transients and contraction. Electromechanical coupling improved with co-culture duration, with 50% of adult-CM coupled after 24 h of co-culture, compared to 19% after 4 h (p = 0.0305). Immobilization with para-nitroblebbistatin did not prevent calcium transient synchronization, with 35% and 36% adult-CM coupled in control and treated samples respectively (p = 0.91), indicating that electrical coupling can be maintained independently of mechanotransduction.
  • Journal article
    Dvinskikh L, Sparks H, MacLeod K, Dunsby Cet al., 2023,

    High-speed 2D light-sheet fluorescence microscopy enables quantification of spatially varying calcium dynamics in ventricular cardiomyocytes

    , Frontiers in Physiology, Vol: 14, Pages: 1-14, ISSN: 1664-042X

    Introduction: Reduced synchrony of calcium release and t-tubule structure organization in individual cardiomyocytes has been linked to loss of contractile strength and arrhythmia. Compared to confocal scanning techniques widely used for imaging calcium dynamics in cardiac muscle cells, light-sheet fluorescence microscopy enables fast acquisition of a 2D plane in the sample with low phototoxicity.Methods: A custom light-sheet fluorescence microscope was used to achieve dual-channel 2D timelapse imaging of calcium and the sarcolemma, enabling calcium sparks and transients in left and right ventricle cardiomyocytes to be correlated with the cell microstructure. Imaging electrically stimulated dual-labelled cardiomyocytes immobilized with para-nitroblebbistatin, a non-phototoxic, low fluorescence contraction uncoupler, with sub-micron resolution at 395 fps over a 38 μm × 170 µm FOV allowed characterization of calcium spark morphology and 2D mapping of the calcium transient time-to-half-maximum across the cell.Results: Blinded analysis of the data revealed sparks with greater amplitude in left ventricle myocytes. The time for the calcium transient to reach half-maximum amplitude in the central part of the cell was found to be, on average, 2 ms shorter than at the cell ends. Sparks co-localized with t-tubules were found to have significantly longer duration, larger area and spark mass than those further away from t-tubules.Conclusion: The high spatiotemporal resolution of the microscope and automated image-analysis enabled detailed 2D mapping and quantification of calcium dynamics of n = 60 myocytes, with the findings demonstrating multi-level spatial variation of calcium dynamics across the cell, supporting the dependence of synchrony and characteristics of calcium release on the underlying t-tubule structure.
  • Journal article
    Damzen M, Xiao H, Jiang X, 2023,

    Alexandrite lasers with blue-diode-pumping

    , Optics Express, Vol: 31, Pages: 5832-5842, ISSN: 1094-4087

    The availability of high-power and high-brightness blue diode lasers makes them attractive as low-cost pump sources for broadly tunable Alexandrite lasers. In this paper we investigate the performance of an Alexandrite laser pumped by a high-power fiber-delivered blue diode module. Output power 1.84 W is achieved, the highest power from blue diode pumped Alexandrite to date. Excellent pump absorption is demonstrated of scrambled pump polarization on both a-axis and b-axis of Alexandrite crystal. Wavelength tuning and dual wavelength operation is produced using the self-birefringent filtering of the Brewster-cut Alexandrite crystal. An analysis is made of laser efficiency and mode formation including the creation of higher-order Laguerre-Gaussian vortex modes (LG01 and LG02). Performance is compared to red diode pumping and prospects for further optimization and power-scaling are discussed.
  • Journal article
    Darling C, Davis SPX, Kumar S, French PMW, McGinty Jet al., 2023,

    Single-shot optical projection tomography for high-speed volumetric imaging of dynamic biological samples

    , JOURNAL OF BIOPHOTONICS, Vol: 16, ISSN: 1864-063X
  • Journal article
    Taylor JR, 2023,

    Fiber Laser Driven Three-Micron Source Development Based on Difference Frequency Generation

    , OPTOELECTRONICS INSTRUMENTATION AND DATA PROCESSING, Vol: 59, Pages: 18-27, ISSN: 8756-6990

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